This invention relates generally to machines for producing optical surfaces on lenses, and more particularly to lathes for cutting such surfaces on plastic contact lenses. Specifically it pertains to a lathe having a controllable, guided, movable cutter.
The introduction of new materials and fitting techniques and growing public acceptance have created an unprecedented demand for plastic optical contact lenses. The methods and machinery available to optical laboratories for surfacing these lenses have not kept pace with this demand. Conventional honing, grinding and polishing methods employed to produce relatively large, glass spectacle lenses do not lend themselves to the production of the diminutive plastic contact lenses. The equipment for carrying out these methods, such as the devices shown and described in U.S. Pat. Nos. 2,392,478, 2,975,565, 3,021,647 and 3,900,971, are ill-suited for processing contact lens blanks, and are particularly unsatisfactory for cutting the relatively new plastic lenses. Some attempts have been made to apply automated milling techniques to the production of plastic contact lens, but tape-programmable mills are costly and require specially trained operators.
Lacking surfacing machines specifically designed for producing plastic contact lenses, attempts have been made to adapt the conventional shop lathe by providing various types of manually operated or powered radius-turning attachments for the cutting tool. These adaptions suffer from a number of dificiencies.
Thus, because conventional lathes swing the cutter around a fixed center of rotation, the finish surface of the lens is cut by a single point of contact of the cutter therewith. This subjects the cutting tool to excessive wear and the tool and workpiece to undue heating. Secondly, they require that the tool post and drive assembly be repositioned each time the radius of the curvature of the optical surface is changed. Such hybrid machines are difficult and time-consumming to set up and need skilled operators to operate and maintain them. Additionally, they are susceptible to harmonically induced vibrations which produce poorly finished lens surfaces requiring extensive timeconsuming polishing. So far as known, none of them is capable of high-volume automated operation, or an ability to cut any continuous complex curved surface such as concave-convex-concave in one cycle of the cutting tool.
Accordingly, a principal object of the subject invention is to provide a lathe for producing plastic contact lenses, wherein the cutting tool moves orthoganally, rather than circularly as in the prior art devices, thereby reducing tool wear and overheating.
Another important object of the invention is to provide a surfacing machine which can be run by semi-skilled operators in the typical optical laboratory so as to produce large numbers of finely finished or precision contoured plastic contact lenses with a minimum labor force.
A further object is to provide a machine of this type which can be manufactured relatively inexpensively and which requires little maintenance and upkeep.
Yet another object is the provision of an automatic or semi-automatic surfacing lathe for plastic contact lenses which utilizes a controllably guided moveable cutter assembly to produce aspheric optical surfaces in a single cutting operation.
Another object is the provision of such a lathe in which the movement of the cutter assembly is precisely guided, throughout the surface-cutting operation.
Yet another object is the provision of a lathe of this type in which the workpiece is secured directly to the spindle of the drive motor, thereby minimizing harmonically induced vibrations and enhancing the surface finish.
The subject invention generally comprises a variable speed, high-torque D.C. motor mounted on an elongated base. An air-activated collet within the motor spindle holds a cylindrical plastic lens blank or "button" in coaxial alignment with the spindle.
A diamond cutter is supported in a vertically adjustable tool post mounted to the upper one of a pair of stacked stages which are adapted for orthonginal linear movement axial and radial of the lens blank, respectively. The lower one of the stages is mounted on a carriage which is itself mounted on the base and arranged for linear movement radial of the workpiece.
In one preferred embodiment, a second variable speed, D.C. motor and a pair of cam-operated X/Y drive mechanisms are mounted on the carriage and drive the stages to move the cutter radially and axially of the rotating lens blank, thereby generating the desired optical surface or surfaces. In an alternative embodiment, individual controlled variable speed motors power the X/Y drive mechanisms through sliding wedges or the like.
In both embodiments, an adjustable stop allows the cutter to be manually centered relative to the axis of rotation of the lens blank. Thereafter, programmable control means automatically position the carriage against the adjustible stop and cycle the cutter thru the lens surfacing operation.